I want to investigate the cation -pi interactions, so that they can be used as required.
Yes, all interactions present in intramolecular contacts do exist in solution. Enthalpic contributions (work needed to separate cation from aromatic ring) are exactly the same, except for some dehydration differences. What can be different is the entropic term; difference in mobility in solution of the separated cation-ring respect with the interacting pair might be huge. This yields a strong difference in free energy and thus in the equilibrium constant of interaction formation. In short, entropic effects promote a higher population of separated cation-ring pairs in solution with respect to intramolecular contacts.
Yes, all interactions present in intramolecular contacts do exist in solution. Enthalpic contributions (work needed to separate cation from aromatic ring) are exactly the same, except for some dehydration differences. What can be different is the entropic term; difference in mobility in solution of the separated cation-ring respect with the interacting pair might be huge. This yields a strong difference in free energy and thus in the equilibrium constant of interaction formation. In short, entropic effects promote a higher population of separated cation-ring pairs in solution with respect to intramolecular contacts.
The existence of the any interactions in the solution is mainly depends on the Enthalpy and entropy. If the binding (interaction) enthalpy is able to compensate the loss of entropy then interaction can exist. in the CATION-PI interaction both interacting partners has vastly varied in their polarity nature. One is polar and other one is non polar.
Non-polar solvents (toulene, benzene, hexane etc) can strongly interact with the PI system and has ability to break the CATION-PI interaction. Polar solvent (Water, MeOH, EtOAc etc) system can strongly interact with the CATION and has ability to break the CATION-PI interaction. So solvent should have optimum polarity nature as CCl4, CH2Cl2 to favors the existence of CATION-PI interactions.
For example CATION-PI interaction between the protonated methylamine and benzene is as follows depending on the solvent used . Gibbs energy (K.Cal/Mol) CCl4,EtOAc, EtOH, H2O: -12.5, -6.2,-5.6,-5.5.
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